Japanese Patent Application Publication No. 2012-30435 discloses a portable printer for printing an image on an image recording medium such as a sheet. According to the disclosed printer, a platen roller and a thermal line head those provided in a housing perform printing on the sheet fed into the housing from an outside.
That is, the sheet is inserted into an interior of the housing through an opening (insertion opening) formed at an upper portion of the housing, and then introduced into a confronting portion between the platen roller and the thermal line head while being guided by a guide member. The thermal line head generates a printing image on the sheet that is conveyed by the platen roller. In this case, sheet conveyance caused by the platen roller and image formation by the thermal line head are controlled on a basis of a result of sheet detection performed by an optical sensor (sheet detection sensor) provided in the housing. A plurality of ribs are provided on an upper surface of the guide member in order to provide smooth sheet conveyance with reducing frictional resistance which may be generated between the sheet and the guide member.